Physicochemical changes in prawns (Machrobrachium rosenbergii) subjected to multiple freeze-thaw cycles

Fresh prawns were subjected to five freeze-thaw cycles (-29°C ⇆ 22°C) and associated physicochemical changes in muscle were determined. Shear force to break prawn tails was dependent on prawn size, more on weight (r = 0.75-0.81) than on diameter (r = 0.56-0.66). No change (P > 0.05) in shear force was observed in raw prawns after five freeze-thaw cycles. However, shear force of cooked prawns decreased after three freeze-thaw cycles which coincided with accelerated lipid oxidation in raw prawns. Electrophoretic analysis revealed gradual decreases in myosin, actin, and most other myofibrillar proteins with each successive freeze-thaw cycle. Enthalpy of protein denaturation decreased from 16.6 J/g (fresh) to 13.5 J/g after one freeze-thaw cycle with minor changes thereafter.